Learn Hardcore Portuguese (Brazil): Você mesmo deve comparar preço e qualidade antes de comprar algo. - You yourself must compare price and quality before buying something.

In Você mesmo deve comparar…, deve can be translated as either “must” or “should”, but in everyday Brazilian Portuguese it usually feels like a strong recommendation / advice, closer to “should” or “ought to”.

Nuance:

Você deve comparar… = You should / ought to compare…
If someone wanted a very strong obligation (like a rule), they might also use deve, especially in written instructions or rules, and then it can sound like “must”.

Compare with:

Você tem que comparar… = You have to compare… (sounds more like a clear obligation in speech)
Você deveria comparar… = You should compare… (a bit softer, more hypothetical; like “it would be good if you compared…”)

So here deve is strong advice, not just a light suggestion, but not as harsh as an order.

Why is there an infinitive after deve? Why deve comparar and not something like “deve a comparar”?

In Portuguese, verbs like dever, poder, querer, precisar (similar to English modals must, can, want to, need to) are usually followed directly by an infinitive, with no extra word in between:

deve comparar = must/should compare
pode comprar = can buy
quer viajar = wants to travel
precisa estudar = needs to study

We do not use a preposition like English “to” (or Spanish a in this position). So you say:

Você deve comparar preço e qualidade.
Never: ✗ Você deve a comparar… or ✗ deve de comparar… in this meaning.

Why is it preço e qualidade without articles? Could I say o preço e a qualidade?

Both are possible, but there is a nuance:

Preço e qualidade (no articles)
- Very common and natural here.
- Refers to price and quality in general, as concepts.
- Sounds neutral and typical in advice sentences.
o preço e a qualidade
- Grammatically correct.
- Sounds a bit more specific: the price and the quality (of a particular product, shop, etc.)
- Could be used if the context is clearer:
  - Você deve comparar o preço e a qualidade deste produto.

In Brazilian Portuguese, direct objects used in a generic or abstract sense often appear without articles:

Gosto de música. = I like music.
Ele estuda medicina. = He studies medicine.

So comparar preço e qualidade = compare (the) price and (the) quality in general.

Why are preço and qualidade singular? Don’t we usually compare many prices?

The singular here is generic / abstract. It is like talking about “price and quality” as categories, not literally one single price and one single quality.

You could also hear:

comparar preços e qualidade = compare prices and quality
comparar os preços e a qualidade = compare the prices and the quality

All of these are possible. The chosen version:

comparar preço e qualidade keeps it short and abstract: “compare price and quality factors” in general.

Why is it antes de comprar and not just antes comprar?

In Portuguese, when antes (“before”) is followed by an infinitive, you must use the preposition de:

antes de comprar = before buying
antes de sair = before leaving
antes de fazer isso = before doing that

So:

Você deve comparar preço e qualidade antes de comprar algo. (correct)
✗ …antes comprar algo. (incorrect)

Think of antes de + verb in the infinitive as a fixed pattern.

Who is the subject of comprar in antes de comprar algo? Is it still você?

Yes. By default, in this structure the subject is the same as in the main clause, unless context says otherwise.

Você mesmo deve comparar preço e qualidade antes de comprar algo.
→ The one who deve comparar (must compare) and who vai comprar (is going to buy) is você.

If you wanted a different subject, you’d normally have to show that clearly:

Você deve comparar preço e qualidade antes de seu filho comprar algo.
= You should compare price and quality before your son buys something.

Without such clarification, antes de comprar algo refers back to você.

Can I omit algo and just say antes de comprar?

Yes. Both are natural:

…antes de comprar algo. = before buying something
…antes de comprar. = before buying (anything/it/whatever you’re going to buy)

A native speaker often drops the object when it’s obvious from context:

Pense bem antes de comprar. = Think carefully before buying.

Adding algo only makes the object explicit as “some (unspecified) thing”, but it doesn’t change the basic idea.

What’s the difference between algo and alguma coisa?

Both mean “something”, but there are differences in register and frequency:

algo
- Slightly more formal / neutral.
- Very common in written language and careful speech.
- Used in your sentence naturally: comprar algo.
alguma coisa
- Very common in everyday spoken Brazilian Portuguese.
- Feels a bit more informal / conversational.
- Example: Você precisa de alguma coisa? = Do you need anything?

In your sentence, you could say:

…antes de comprar algo. (perfectly fine)
…antes de comprar alguma coisa. (also fine, a bit more chatty)

Can mesmo go in a different place? What changes if I say Você deve mesmo comparar preço e qualidade?

Yes, moving mesmo changes its function and meaning.

Você mesmo deve comparar preço e qualidade…
- mesmo emphasizes “você” = you yourself
- Meaning: you, personally (not someone else), should compare.
Você deve mesmo comparar preço e qualidade…
- Here mesmo functions more like “really / indeed”.
- Meaning: you really should compare price and quality.
- The emphasis is on the degree of obligation, not on who does it.

So:

Você mesmo deve… → emphasis on who.
Você deve mesmo… → emphasis on how strongly you should do it.

Is Você mesmo deve… polite and natural in Brazilian Portuguese?

Yes, it is both natural and neutral in terms of politeness.

Você is the standard informal/polite singular “you” in most of Brazil.
mesmo here just adds emphasis (“you yourself”), not rudeness.

If you want to be more formal, especially with older people or in professional contexts, you might replace você with:

O senhor (to a man)
A senhora (to a woman)

For example:

O senhor deve comparar preço e qualidade antes de comprar algo.
(Very polite / formal)

Could I use tu instead of você in this sentence?

Yes, in regions where tu is commonly used (for example, much of the south and some parts of the northeast), people might say:

Tu mesmo deves comparar preço e qualidade antes de comprar algo. (more “standard” agreement)
Or in colloquial speech: Tu mesmo deve comparar preço e qualidade… (common in some areas, even though it mixes tu with deve)

Key points:

você
- deve (3rd person): Você deve comparar…
tu
- deves (2nd person): Tu deves comparar… (grammatically standard, less common in many spoken varieties)

Is the word order fixed, or could I say Antes de comprar algo, você mesmo deve comparar preço e qualidade?

You can definitely change the word order like that; both are correct:

Você mesmo deve comparar preço e qualidade antes de comprar algo.
Antes de comprar algo, você mesmo deve comparar preço e qualidade.

Putting Antes de comprar algo at the beginning just emphasizes the condition / time (“Before buying anything…”). It’s very natural in instructions, advice, or warnings. The basic grammar and meaning stay the same.